1. Field of the Invention
This invention relates to cable pulling systems and, more particularly, to a system for drawing a mole through a composition to create a passageway between first and second spaced locations.
2. Background Art
It is well known in the industry to draw a mole through a composition to define a passageway through the composition between first and second spaced locations. It is known to use this method to replace collapsed conduits, such as those used for sewage, or for other applications. To carry out this process, access space is required at each of the first and second locations. A cable is directed from the second location through the existing conduit back to the first location at which the cable end is connected to an appropriately configured mole. The mole is engaged with a length of a replacement conduit in such a manner that the conduit will follow translatory movement of the mole. At the second location, a cable pulley mechanism is employed. The cable pulley mechanism, which is commonly hydraulically actuated, is braced against the composition and operated to draw the mole through the composition from the first location to the second location. The operator, who is situated at the second location, must monitor the advancement of the mole and disable the cable pulling mechanism at the appropriate time to prevent the mole from detrimentally contacting any part of the cable pulling mechanism and/or its support structure.
One known cable pulling mechanism is disclosed in U.S. Pat. No. 6,305,880. In that mechanism, the mole is advanced, through repeated pulling strokes, over its entire travel path between the first and second locations. In a typical pulling cycle, the mole will be advanced on the order of four inches. Each successive cycle must be initiated by an operator. While this system has been commercially successful, it has a number of inherent drawbacks.
First of all, as a result of the stepwise application of the pulling force, the mole, and following conduit, come to rest each time the mechanism is at the dwell stage for a pulling cycle. As this occurs, the stationary mole and conduit may become temporarily lodged before the pulling force can be reapplied thereto. To reinitiate movement of the mole, a greater force may be required than would be if the mole movement were not interrupted. This places greater demands on the cable pulling structure, the cable, the mole, the conduit, and the structure operatively connecting the mole to the cable and conduit. As a result, there is the potential for premature failure of one or more of these components and a potential reduction in the anticipated life of the overall system.
To address this problem, the system components may be made with increased capacity to ensure reliable operation and an adequately long life for the equipment. This may significantly increase the overall system costs which may have to be passed on to the system purchaser.
Another problem with the above prior art system is that the cable pulling mechanism is required to have potentially a large number of components to coordinatingly interact to alternatingly apply and release the pulling force on the cable. Generally, the more complicated systems become, the more prone they are to malfunction. Further, complicated systems are inherently more expensive than their simpler counterparts.
Still further, the above system has the drawback that the process for moving the mole between the first and second locations may be time consuming by reason of the stepwise advancement of the mole. These types of systems are generally designed to advance a mole through relatively dense compositions that offer a high resistance to movement of the mole. In some environments, such as in loose soil, a significantly lesser resistance to mole movement may be encountered. However, the system operator is nonetheless required to operate the system in the same manner, initiating each advancing cycle, so that the mole moves at a relatively slow rate from the first location to the second location. Since these systems may require two or more individuals to set them up and monitor their operation, the number of man hours required to complete a job may be significant.
Designers of this type of system strive to devise systems that can be economically manufactured, will reliably perform in potentially severe environments, can be conveniently and efficiently set up, operated, and broken down, and will perform reliably for an adequate lifetime. In the interest of economy, it is also a goal for designers of these systems to avoid the unnecessary expenditure of man hours for their operation.